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  <a href="http://sudopedia.enjoysudoku.com/Uniqueness_Test.html#Uniqueness_Test_1">Uniqueness Test 1</a>
   <p>
   The {5} <b>cells {3}</b> form a <b>unique {0}</b> with two common <b>candidates {1} and {2}</b>.
   There are two possibilities to place the two digits into the {5} cells which leads to an invalid puzzle with two solutions.
   This <a href="http://sudopedia.enjoysudoku.com/Deadly_Pattern.html">deadly pattern</a> must be avoided because a valid puzzle can have just one solution.
   To avoid the deadly pattern extra candidates in one or several of the {5} cells exist to eliminate other candidates in the puzzle. 
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   <p>
   The highlighted <b>cell {4}</b> is the only cell with extra candidates. One of those highlighted candidates must go into <b>cell {4}</b> to avoid the deadly pattern.<br/>
   Therefore the <b>candidates {1} and {2}</b> can be removed from <b>cell {4}</b>. 
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